The present invention relates to a modular unit for insertion into HF-tight housings of electronic equipment, the modular unit including a circuit board equipped with electronic components, a front plate having a U-shaped cross section and being provided on its one side with a longitudinal web and on its opposite side with a longitudinal strip that is parallel to the longitudinal web and has an insertion slope. Spring elements are provided at the longitudinal web and, when the modular unit is inserted, lie electrically conductively against the longitudinal strip of the front plate of the adjacent modular unit.
The invention is used in connection with modular units for electronic and electrical equipment constructed of modular systems and is employed in conjunction with housings or closed modular unit carriers for which a very high shielding effect is required against electromagnetic influences or which enclose components that cause electromagnetic interferences which must not be permitted to escape.
The use of HF-tight housings and the measures for appropriate shielding are known per se. In the housings, separating grooves are avoided wherever possible or are closed off by electrically contacting seals, wire braids or electrically conductive sealing cords. However, problems are caused by the unavoidable gaps between the parts that are to be inserted and pulled out of the housings, namely the accessory inserts and cassettes of plug-in modular units which are arranged next to one another in the housings and whose juxtaposed front plates form the frontal face of the housings.
To seal the gaps between U-shaped front plates of modular units it is known to provide narrow spring strips at their one longitudinal edge so as to establish electrical contact with the edges of the respectively adjacent front plates once they are inserted (German Utility Model Patent 88/03,544, U.S. Pat. No. 4,631,641); however, after repeated insertion and removal of the modular units, the contacts furnished by the narrow spring strips are no longer very reliable, the short spring leaves soon exhibit fatigue.
German Unexamined Published Patent Application 3,604,860 further proposes to equip the rear face of the front plate to be sealed with a longitudinal strip and with an oppositely disposed longitudinal web which is provided with two adjacent, longitudinal grooves that are set at a right angle to one another. The rear face of a curved sliding spring strip is clamped into these longitudinal grooves and its free end is supported on the base of the longitudinal web so as to slide along the base when compressed. Although the sliding movement provides for self-cleaning of the contact faces, the active spring leg is only rather short due to its contact, which adversely affects the reliability of the established contact.
A two-part, high frequency tight housing is known in which a plurality of juxtaposed spring metal strips having resilient tongues are to ensure good contact between the bottom portion of the housing and the cover. Due to the short structural length of the spring leaves, however, fatigue phenomena will be unavoidable if the cover is opened and closed frequently (German Unexamined Published Patent Application 3,523,770).
Additionally, a shielded housing for electrical devices is known whose door, at the face where it contacts the housing, carries a plurality of contact spring arrangements that are subdivided into segments. In order to hold the juxtaposed contact springs, the door frame has a special configuration which includes a longitudinal slot and a U-shaped angle into which the contact springs are clamped in a form-locking manner. However, this sealing arrangement is not suitable as a HF seal for the front plates of modular units (German Published Patent Application 2,247,005).